The present invention relates to a data transmission system for a portable terminal when the terminal body is separated from peripheral device.
Conventionally, a communication system by radio has been used. FIGS. 1A to 1C show an arrangement of the conventional data transmission system of a portable terminal. FIG. 1A shows the entire arrangement; FIG. 1B shows the arrangement of the transmission section; and FIG. 1C shows the arrangement of the receiving section. In FIGS. 1A to 1C, a portable terminal 51 is connected with a printer 52 by radio. In the transmission section, transmission data are supplied from a control unit 53 to a radio converter unit 55 through a transmission data storage unit 54 which converts the signal into radio to be sent out as a radio wave output. In the receiving section, a radio demodulation unit 56 receives and demodulates a radio wave input to be supplied to a received data holding unit 57, and finally a control unit 58 analyzes the received data.
FIG. 1D shows the data format in the conventional data transmission system. Transmission data 61 include data of "abcdefghij . . . ". Final data E1 and E2 represent data for checking. Where the transmitted data cannot be received owing to external noise 62, received data 63 include the portion of ? corresponding to "fghi". This makes it impossible to receive the transmission data correctly. Even if the transmission data are transmitted again, the external noise generated still does not permit correct communication.
In this way, in the conventional radio communication system, a great number of transmission obstacles due to external noise are generated during the communication. As the case may be, therefore, even if the transmission is repeated many times when the obstacle is generated, communication cannot be realized. As a result, in the radio communication which is always influenced by the external noise, it is an important point how the influence by the external noise should be prevented.